In an alternate current, since there is a phase difference between voltage and current, reactive power is caused due to the difference. Along with measurement of active power which is power consumption of an induction motor and energy-saving efforts, it is increasingly important to visualize electrical power by measuring reactive power, apparent power, power factor, and the like, from the viewpoint of thorough effective utilization of energy.
Power consumption in an induction motor varies largely according to input voltage, input current, frequencies, and the magnitude of a load. Conventionally, current, voltage, and a phase difference (θ) of “current-voltage” are measured separately, and then “voltage*current*power factor (cos θ)” is calculated by an arithmetic operation.
In order to measure power consumption, systems using current transformer (CT) and shunt resistance have been used widely as means for measuring current. However, current transformer (CT) involves restrictions on the installation space, and is expensive. Accordingly, it is not easy to use CT when power consumption is desired to be measured in various locations. On the other hand, a shunt resistance system involves restrictions on the installation space, consumes energy wastefully, and incidentally leaves a heating problem.
Meanwhile, as a smaller power meter, one using a Hall element has been proposed conventionally. In Patent Literature 1, active power, reactive power, phases, and power factor are measured using two Hall effect elements. In Patent Literature 2, when measurement is performed by a Hall effect element, electrical power of a load is measured accurately by considering effects of a self-magnetic field error term caused by the generated control current.